My introduction to JPEG-XL was by 2kliksphillip on YouTube, he has a few really good analyses on this topic, including this video: https://youtu.be/FlWjf8asI4Y
It's a huge piece for sure, but not the only one. For example, Firefox and Windows both don't support it out of the box currently. Firefox requires nightly or an extension, and on Windows you need to download support from the Microsoft store.
blink-dev mailing list
https://groups.google.com/a/chromium.org/g/blink-dev/c/WjCKc...
Tracking Bug (reopened)
https://issues.chromium.org/issues/40168998